1. Field of the Invention
The present invention relates to a hybrid heat pump system and, more particularly, to a heat pump system that utilizes a combination of a conventional heat pump and a membrane permeator flow device for conditioning gas, preferably air, within an either enclosed or open space before the gas is treated by the heat pump.
2. Description of the Prior Art
Humidity has an effect upon a building. As humidity increases, so does the presence of bacteria, mold and mildew. Therefore, having an ability to control humidity and lower its level will contribute to an elimination of microorganism propagating environments. For example, refrigeration air conditioner systems in humid environments are often inadequate with respect to acceptable humidity control, with or without refrigeration incorporated therein. In wet or damp environments refrigeration air conditioner systems utilizing refrigerant cooled air coils are often overtaxed and their efficiency adversely affected. Humidity control becomes an important factor, not only as related to human comfort, health and structural deterioration, etc., but also as to adequacy of dehumidification and its efficient application.
A heat pump is a system that utilizes a thermodynamic process for taking thermal energy from a low temperature heat source and releasing it at higher temperature utilizing an input of energy from another source. A significant problem with heat pumps is that under certain circumstances an outdoor coil will, during a heating mode of operation, have frost accumulate thereon. Efficient operation of the system requires that sufficient heat be transferred from air flowing through an outdoor heat exchanger to maintain adequate capacity to meet a heating demand in a comfort zone. If the outdoor ambient air temperature is less than approximately 32xc2x0 F., frost and ice may accumulate on the heat exchanger, blocking air flow therethrough to such an extent that its capacity for heat transfer is reduced below that required to meet the heating demand in the comfort zone. As the frost thickness increases, the overall efficiency of the system decreases dramatically, and energy is wasted. Accordingly, many schemes have heretofore been proposed for detecting the frost and for taking corrective action for removing the frost from the outdoor coil. Examples of prior art systems include U.S. Pat. Nos. 3,170,304, 3,170,305, 3,400,553, 4,373,349, 4,102,389, 4,209,994, 4,406,133 and 5,507,154.
Two significant factors that determine a rate of accumulation of frost on an outdoor coil during the system-heating mode are relative humidity and temperature of the outdoor air. Some prior art systems have attempted to solve the defrost problem by programming a fixed length of time of running a compressor before initiation of a defrost mode of operation based on an assumed value of outdoor air temperature. It has been a common practice to activate a reversing valve and remove heat from the system, xe2x80x9cdumpingxe2x80x9d the heat into the outdoor coil to melt the ice. The equipment has usually been left in this defrost mode until the coil temperature reached 75xc2x0 F. This causes a serious waste of energy. Also, the defrost action is frequently accomplished by reversing the main system to a xe2x80x9ccoolingxe2x80x9d mode. This causes relatively hot refrigerant to be directed to the outdoor coil to melt the accumulated frost. However, this also causes cooling of the controlled building which is in turn typically offset by a use of high cost, lower-efficiency, electric resistance heating. Again, energy is wasted.
The accumulation of frost on evaporator coils of either a home or commercial refrigerator has been recognized as a problem for many years. To overcome the problem, defrost systems have been developed, some of which have been commercially successful. Examples of prior art systems include U.S. Pat. Nos. 3,084,520, 3,126,716, 3,499,295, 4,122,687, 5,406,805 and 5,867,994. Solutions suggested in these patents include additional heating, a dual evaporator or changes in air circulation.
The addition of heat to the system thus utilizes energy to melt ice on the coils and energy to cool the refrigerator to the extent of heat added by the heating coils. Thus, there is a substantial increase in energy requirements in the defrost step and in the subsequent cooling step, as a result of using heating for defrosting the evaporator coils.
Systems with two evaporator coils alternately cool the air passing therethrough. Such systems require complex valving for the refrigeration fluid and add some heat from the refrigeration fluid to the defrost coils.
In a system that change air circulation, a refrigeration unit has a defrost system that defrosts the evaporator coil by passing warmer air across the evaporator coil to heat the defrosting air. Although such a system offers an improvement, it still consumes additional energy.
Desiccation is a process of removing vapor of one or more liquids out of a gas containing the vapor, resulting in vapor depleted or dry gas. Usually this is done by adsorption material such as zeolites or silica gel. However it can be done by absorption, for example, absorption of water vapor by sulfuric acid.
To overcome the moisture problem in refrigeration, several inventors have suggested hybridization of a heat pump with a desiccation system. U.S. Pat. No. 4,941,324 describes a hybrid air conditioning system that simultaneously dehumidifies and cools air using standard vapor-compression equipment and aqueous solutions of liquid desiccant. U.S. Pat. Nos. 4,700,550, 5,517,828, 5,551,245 and 5,816,065 describe hybrid air pump systems that combine solid desiccation systems mostly in the form of a rotatable moisture transfer wheel with desiccant material, and a rotatable heat exchange wheel with heat pumps that include an evaporator, compressor, condenser and metering device operatively coupled by a refrigerant circulating line for evaporation of refrigerant and transfer of heat to the refrigerant.
Using desiccant systems for removing moister from the processed gas or air is subject to several limitations. The process of dehumidification with desiccant adds heat to a column of air being treated, it being desirable to remove this heat before it reaches the refrigeration cooling coil. The process of dehumidifying with desiccant requires the regeneration or strengthening of a weakened moisture laden desiccant. This process requires an application of heat to the desiccant material and requires either alternating desiccation regeneration cycles or use of a mechanically cumbersome desiccant wheel.
A membrane is a semi permeable barrier capable of selectively permeating certain constituents our of fluid mixture. A membrane permeator is a self contained assembly of membrane packaging, including all required housings and piping components, capable of rendering perm selective separation of a fluid mixture.
A membrane separation method for removing water vapor in gases is a method in which a gas containing water vapor is contacted to one side of a vapor permselective membrane assembly, and a dry gas is contacted to the other side of the membrane. The water vapor is selectively permeated and separated through the membrane. In principle, it has merits over other methods such that running cost is low, the structure of the apparatus is simple, and dry air can continuously be obtained without polluting the air.
As a vapor permselective membrane for permeability of water vapor, an ion exchange membrane as well as a dehumidifying method using such membrane have been proposed by U.S. Pat. Nos. 3,735,558 and 4,909,810. Hollow fiber membrane-based dehydration is also known. See, for example, U.S. Pat. Nos. 4,783,201, 4,725,359, 4,718,921, 4,497,640, 4,583,996 and 3,511,031. U.S. Pat. No. 4,900,626 discloses a hollow composite fiber for dehydration having a polydimethylsiloxane coating on a dense layer of the fiber support.
Although membranes have been used in various separation applications, their use for heat pump systems has been limited. U.S. Pat. Nos. 4,152,901 and 5,873,260 propose to improve an absorption heat pump by using of semipermeable membrane and pervaporation membrane respectively. U.S. Pat. No. 4,467,621 proposes to improve vacuum refrigeration by using sintered metal porous membrane, and U.S. Pat. No. 5,946,931 describes a cooling evaporative apparatus using a microporous PTFE membrane.
There is a need for a versatile multi-use dehumidifier unit adapted to pre-condition air in conjunction with a refrigeration air conditioning system. In such a dehumidifier unit, optimum humidity is attained in differing climatic conditions and operates efficiently either alone or in combination with the refrigeration air conditioning system.
It is an object of the present invention to provide a novel membrane desiccation heat pump system that is useful for various application such as cooling, chilling, heating and air conditioning, and that is low cost efficient and simple to maintain.
It is another object of the present invention to provide a hybrid heat pump system, which has an energy economy and an efficiency better than other kind of heat pumps. One important feature of the present invention resides in the fact it employs a process that is carried out without an addition of costly heat energy from an external source.
Another object of the present invention is to provide a hybrid heat pump for an air conditioning system, and for heating and cooling, that permits a greater degree of independent control of temperature and humidity for achieving parameter levels in desired regions of a comfort zone.
It is a further object of the present invention to provide a versatile dehumidification system adaptable to efficient operation in diverse climatic conditions, in combination with an air refrigeration system. A feature of such an air pre-conditioner unit when combined with an air-conditioned refrigeration system is increased efficiency of the refrigeration system.
It is still a further object of the present invention to provide a hybrid heat pump system capable of working in a reverse mode for heating operation with a frost free heat taking capability from a low temperature heat source under diverse temperature and moisture conditions.
Another object of the present invention is to provide a hybrid heat pump-based liquid chilling and heating reverse cycle chilling (RCC) process system usable for various applications.
Still another object of the present invention is to provide a frost-free refrigeration system operating at a low cost and high reliability, both for commercial and domestic applications.
These and other objects of the present invention are achieved by a hybrid heat pump system. The system includes (i) a membrane perneator having a permselective membrane capable of selectively removing vapor from a vapor-containing gas to yield a dry gas, (ii) a heat pump having (a) an internal side for exchanging thermal energy with a process fluid, (b) an external side for exchanging thermal energy with an external environment, and (c) a thermodynamic mechanism for pumping thermal energy between the internal side and the external side in either direction, (iii) means for conveying the vapor-containing gas into the membrane permeator, and (iv) means for routing the dry gas to either of the internal side or the external side.
The present invention also contemplates a method for treating vapor-containing gas. The method includes the steps of (i) selectively removing vapor from the gas, to yield a dry gas, using a membrane permeator having a vapor permselective membrane, (ii) bringing the dry gas in contact with either of (a) an external side of a heat pump, or (b) an internal side of the heat pump, wherein the internal side exchanges thermal energy with a process fluid, and wherein the external side exchanges thermal energy with an external environment; and (iii) employing a thermodynamic process to pump thermal energy between the internal side and the external side.
The present invention relates to a hybrid heat pump for use in association with a gaseous flow system adapted to move a gaseous process fluid such as air, containing moisture vapor. The hybrid system includes a heat pump of any type unit used for either cooling or heating, combined with a moisture vapor membrane permeator, and means for passing the process fluid through the membrane permeator to dry the process fluid and substantially reduce the moisture vapor in the process fluid, vapor removal means for removing the concentrated vapor from the membrane permeator, thereby separating the vapor from the gaseous process fluid circulating in the system. The use of the membrane perneator substantially reduces a condensable load from a heat taking side of the heat pump and prevents accumulation of the condensable load on the heat taking side. Further, because of the use of the membrane permeator combined with the heating unit and/or the cooling heat pump in the unit, the heat pump can achieve a better thermal efficiency and better reliability of operation.
A feature and advantage of the present invention is that the hybrid heat pump permits operation under conditions of temperature and moisture with out using extra energy to handle such conditions. Thus, the present invention provides a very efficient heat pump for the purpose of either cooling or heating.
A principle component of the present invention is its employment of a membrane separation process for removal of vapor from a stream of carrier gas. Removal of the vapor from the gas stream is also the removal of the latent heat contained in this vapor thus providing the thermodynamic vehicle for the heat pump.
A membrane suitable for the present invention must be capable of an efficient and economical separation of vapor from the carrier gas. Such a membrane separator assembly may come in different shapes and forms. The following paragraphs describe features of a membrane assembly suitable for use for vapor separation in the present invention.
The membrane assembly may include one or more membrane units that could be assembled in any array, such as series, parallel, cascade or a membrane column. A membrane unit may be either a self-contained module or a combination of one or more membrane elements in a housing. A membrane element can be in any form of packaging of membrane area in a single item such as, but not limited to, module, cartridge, plate, etc.
The membrane could be solid or liquid, organic or inorganic, pre-made or dynamic, charged or uncharged, ionic or non-ionic, hydrophilic or hydrophobic, porous or dense, permeable, non-permeable or semi permeable. It could be polymeric, metallic, ceramic, carbon or glass. Membrane geometry could be in any form such as flat sheet, tubular, capillaries, hollow fibers or a monolith. A membrane element could be in any configuration such as hollow fiber module, hollow fiber plates, spiral wound module, plate and frame, pleated or folded cartridge, envelopes, bags, tubes and sheets, spiral tubes, candles or monolithic.
Vapor permeates through a membrane from a feed side of the membrane to a permeate side of the membrane. A flow pattern of either a feed-retentate side or a permeate side of the membrane in the membrane unit may be counter-current, co-current or both. It could be transverse flow, diagonal flow or random direction flow. It could be unidirectional or multi directional. It could be one pass or multi pass. Either flow could be on any side of the membrane in the element configurations.
Removal of the permeating vapor from the membrane unit may be direct or may be facilitated by means such as reflux flow, either internal or external, vacuum and/or condensation. It could be a sweep stream that may be of gas or liquid. Such a sweep stream may be inert or reactive, i.e., having either physical or chemical affinity toward the permeating vapor.
A membrane for vapor separation from gas especially dehydration is preferably capable of removing water vapor from the feed gas to a desired dew-point, the water vapor separation takes place with as little loss of feed gas to the permeate as possible and the process economically perform this separation. In other words, the membrane surface area required to perform a given water vapor separation should be as small as possible.
A driving force for a transport of vapor through the membrane is a partial pressure differential of the vapor across the membrane. Therefore, a partial pressure of water vapor in a gas leaving as permeate from a membrane module cannot exceed a partial pressure of water vapor in a feed gas entering the membrane module. In most cases, the partial pressure of water in a gas at saturation is very low. Therefore, the partial pressure driving force for the vapor transport must be provided by one of three methods: (1) a sweep method, in which dry gas from an external source is swept proximate to the permeate side of the membrane; (2) a vacuum method, in which a vacuum is applied to the permeate side of the membrane; or (3) a dilution method, in which (a) the permeate is left at, for example, atmospheric pressure, but either a small percentage of the feed gas is allowed to permeate the membrane, diluting the water vapor content of the permeate, or (b) reflux of a part of the dry retentate into the permeate compartment. In all three cases, the driving force for the permeation of the vapor in the feed gas is provided by the vapor partial pressure difference between the feed and the permeate.
The hybrid heat pump can be constructed in several configurations. It may be either an open cycle or close cycle gas system, and it may be either an open cycle or close cycle liquid system. The system may be operated either in a cooling mode or in a heating mode. It may also determine both the temperature and the vapor content of the out put gas. Specifically, the hybrid heat pump may serve as a very efficient air condition system both for large sizes and small sizes, and it may be an excellent system for providing frost-free refrigeration for various applications.
As in any heat pump, the laws of thermodynamics govern the hybrid heat pump. It removes heat from a media at a low temperature and transfers it to a higher temperature by investing external energy into the process. However it performs its tasks more efficiently, owing to the reduced load of condensable vapor on the heat taking side of the heat pump.
Another major component of the membrane desiccation heat pump is the heat pump. The heat pump may be of a type from any of the following groups:
(a) a mechanical, e.g., compression refrigeration, heat pump such as a gas expansion cycle or a vapor compression cycle, single or multi-stage single or binary fluid cycles, scroll type, screw type, rotary type, swash plate type, Stirling type, Rankin cycle type, Brayton cycle type or Cascade refrigeration cycle;
(b) an absorption refrigeration heat pump, such as an intermittent cycle or continuous process;
(c) evaporative cooling refrigeration such as vacuum refrigeration or centrifugal compression system;
(d) a solid carbon dioxide process;
(e) a thermoelectric cooling element, e.g., an electronic heat pump; and
(f) a desiccant heat pump, a desiccant bed type, a desiccant wheel type or a liquid desiccant system.
Such a heat pump has an internal side that exchanges energy with the fluid to be processed, an external side, that exchanges energy with the outside ambient environment, and a thermodynamic mechanism to pump energy from one side to another in either direction.
The hybrid heat pump of the present invention works in either a cooling mode or a reverse heating mode. It can be utilized for air conditioning, chilling and heating, and commercial, domestic or industrial commercial and cryogenic applications. The hybrid heat pump serves as an excellent system for providing chilling or heating in reverse cycle chilling (RCC) for various applications.